1. Discovering Cells Chapter 1 Section 1

2. Think about this… A majestic oak tree shades you on a sunny day at the park. A lumbering rhinoceros wanders over to look at you at the zoo. After a rain storm, mushrooms sprout in the damp woods. What do you think an oak tree, a rhinoceros, and a mushroom have in common? You might say that they are all living things. What makes these living thing alike? They are all made up of cells.

3. Cells Cells are the basic units of structure and function in living things. Just like bricks are the building blocks of a house or school, cells are the building blocks of life. Because you are alive, you are made up of cells.

4. Take a look Since you are alive, you are made of cells too. Look closely at the skin on your arm. No matter how hard you look with your eyes alone, you won’t be able to see individual skin cells. The reason for this is that cells are very small. In fact, one square centimeter of your skin’s surface contains over 100,000 cells.

5. First Sighting of Cells Until the late 1500s there was no way to see cells No one even knew that cells existed. Around 1590, the invention of the microscope enabled people to look at very small objects. The invention of the microscope made it possible for people to discover and learn about cells. A microscope is an instrument that makes small objects look larger.

6. Microscopes Some microscopes use lenses to focus light. The lenses used in light microscopes are similar to the clear curved pieces of glass used in eyeglasses. A simple microscope contains only one lens. A hand held lens is an example of a simple microscope. A light microscope that has more than one lens is called a compound microscope.

7. Robert Hooke One of the first people to observe cells was the English scientist and inventor Robert Hooke. In 1663, Hooke observed the structure of a thin slice of cork using a compound microscope that he built himself. Cork is the bark of the cork oak tree which makes it alive so it made up of cells. To Hooke, the cork looked like tiny rectangular rooms, which he called cells. What most amazed Hooke, was how many cells the cork contained. He calculated that a cubic inch piece of cork had about twelve hundred million cells.

8. Anton van Leeuwenhoek At about the same time Hooke made his discovery, Anton van Leeuwenhoek also began to observe tiny objects with microscopes. Leeuwenhoek was a Dutch businessman and amateur scientist who made his own lenses. He used the lenses to construct simple microscopes. Leeuwenhoek used his microscope to look at pond water. He was surprised to see one-celled organisms, which he called animalcules, meaning little animals. Leeuwenhoek went on to look at many other specimens including scrapings of teeth and became the first person to see tiny single- celled organisms known as bacteria.

9. Schleiden and Schwann Over the years and through increased improvements to the microscope, scientists have discovered that all kinds of living things were made of cells. In 1838, Matthias Schleiden, a German scientist concluded that all plants are made of cells. The next year, another German scientist, Theodor Schwann concluded that all animals are also made of cells. Although, Schleiden and Schwann made important discoveries about living things, they did not understand where cells came from.

10. Rudolf Virchow In 1855, a German doctor, Rudolf Verchow (FURkoh) proposed that new cells are formed only from existing cells. “All cells come from cells” wrote Virchow. The observations and conclusions of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things.

11. The Cell Theory The cell theory states: All living things are composed of cells. Cells are the basic unit of structure and function in living things. All cells are produced from other cells.

12. How a Light Microscope Works Magnification: The first property, magnification, is the ability to make things look larger than they are. The lens or lenses in a light microscope magnify an object by bending the light that passes through them. Convex lens – A lens that is thicker in the center than the edges. The light passes through the sides of the lenses and bends inward. When the light hits the eye, the eye sees the object as larger than it really is.

13. Compound Microscope Because a compound microscope uses more than one lens, it can magnify an object even more. Light passes through a specimen and then through two lenses. The first lens near the specimen magnifies the object. The second lens near the eye further magnifies the enlarged image. The total magnification of the microscope is equal to the magnifications of the two lenses multiplied together. For example lens one has a magnification of 10 and lens two has a magnification of 20. The total magnification of the microscope is 10x20 = 200.

14. Resolution To create a useful image, a microscope must also help you see individual parts clearly. The ability to clearly distinguish the individual parts of an object called resolution. For example, when you use your eyes to look at a photo printed in a newspaper, it looks like a complete picture from one side to the other. The picture, however, is really made up of a collection of small dots. To the unaided eye, two tiny dots close together appear as one. If you looked at the photo under a microscope, you would see the dots. This is because the microscope improves resolution.

15. Electron Microscope An electron microscope uses a beam of electrons instead of light to examine a specimen. Electrons are tiny particles that are smaller than atoms. Because they use tiny electrons to produce images, the resolution of electron microscopes is much better than the resolution of light microscopes. As the technology of microscopes keeps improving, scientists will continue to learn more about the structure and function of cells.